10,729 research outputs found
A CLEAN-based Method for Deconvolving Interstellar Pulse Broadening from Radio Pulses
Multipath propagation in the interstellar medium distorts radio pulses, an
effect predominant for distant pulsars observed at low frequencies. Typically,
broadened pulses are analyzed to determine the amount of propagation-induced
pulse broadening, but with little interest in determining the undistorted pulse
shapes. In this paper we develop and apply a method that recovers both the
intrinsic pulse shape and the pulse broadening function that describes the
scattering of an impulse. The method resembles the CLEAN algorithm used in
synthesis imaging applications, although we search for the best pulse
broadening function, and perform a true deconvolution to recover intrinsic
pulse structre. As figures of merit to optimize the deconvolution, we use the
positivity and symmetry of the deconvolved result along with the mean square
residual and the number of points below a given threshold. Our method makes no
prior assumptions about the intrinsic pulse shape and can be used for a range
of scattering functions for the interstellar medium. It can therefore be
applied to a wider variety of measured pulse shapes and degrees of scattering
than the previous approaches. We apply the technique to both simulated data and
data from Arecibo observations.Comment: 9 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
pulsar_spectra: A pulsar flux density catalogue and spectrum fitting repository
We present the pulsar_spectra software repository, an open-source pulsar flux
density catalogue and automated spectral fitting software that finds the best
spectral model and produces publication-quality plots. The Python-based
software includes features that enable users in the astronomical community to
add newly published spectral measurements to the catalogue as they become
available. The spectral fitting software is an implementation of the method
described in Jankowski et al. (2018) which uses robust statistical methods to
decide on the best-fitting model for individual pulsar spectra. pulsar_spectra
is motivated by the need for a centralised repository for pulsar flux density
measurements to make published measurements more accessible to the astronomical
community and provide a suite of tools for measuring spectra
Cosmic ray produced Mg<SUP>28</SUP>, Si<SUP>31</SUP>, S<SUP>38</SUP>, C<SUP>l38</SUP>, Cl<SUP>34m</SUP> and other short-lived radioisotopes in wet precipitation
The concentrations of seven radioisotopes, expected to be produced in the troposphere by interactions of secondary cosmic rays with atmospheric nuclei, have been measured in "fresh" rain collections. The half-lives of these isotopes range from about half an hour to a day. The procedures developed for rapid, specific and sensitive analyses of these nuclides are discussed. Detection of two of the isotopes studied, Cl39 (half-life: 55 mins.) and Na24 (15 hrs.), has been reported earlier by Winsberg and Rodel respectively. Amongst the remaining nuclides, two: S38 (2.9 hrs.) and Cl38 (37.3 mins.) were independently and almost simultaneously detected by us and Perkins and his collaborators. Three other isotopes, Cl34m (32 mins.), Si31 (2.6 hrs.) and Mg28 (21.2 hrs.), detected in the present work have not yet been reported elsewhere. The nature of cosmic ray secondary particles responsible for the production of these short-lived radionuclides in the troposphere is discussed. Isotope production is found to vary strongly with altitude in the troposphere; it increases by a factor of two every 1.5-2 km depending on the radioisotope under question. This fact combined with the availability of several isotopes of half-lives ranging from about half an hour to a day leads to the possibility of using them as tracers for studying short-term tropospheric processes, e.g. those occurring prior to and during condensation in a precipitating cloud. The implications of the present measurements are discussed
The High Time Resolution Universe Survey - V: Single-pulse energetics and modulation properties of 315 pulsars
We report on the pulse-to-pulse energy distributions and phase-resolved
modulation properties for catalogued pulsars in the southern High Time
Resolution Universe intermediate-latitude survey. We selected the 315 pulsars
detected in a single-pulse search of this survey, allowing a large sample
unbiased regarding any rotational parameters of neutron stars. We found that
the energy distribution of many pulsars is well-described by a log-normal
distribution, with few deviating from a small range in log-normal scale and
location parameters. Some pulsars exhibited multiple energy states
corresponding to mode changes, and implying that some observed "nulling" may
actually be a mode-change effect. PSRJ1900-2600 was found to emit weakly in its
previously-identified "null" state. We found evidence for another state-change
effect in two pulsars, which show bimodality in their nulling time scales; that
is, they switch between a continuous-emission state and a single-pulse-emitting
state. Large modulation occurs in many pulsars across the full integrated
profile, with increased sporadic bursts at leading and trailing sub-beam edges.
Some of these high-energy outbursts may indicate the presence of "giant pulse"
phenomena. We found no correlation with modulation and pulsar period, age, or
other parameters. Finally, the deviation of integrated pulse energy from its
average value was generally quite small, despite the significant phase-resolved
modulation in some pulsars; we interpret this as tenuous evidence of energy
regulation between distinct pulsar sub-beams.Comment: Before full MNRAS publication, supplementary material is available
temporarily at http://dl.dropbox.com/u/22076931/supplementary_material.pd
Scintillation arcs in low-frequency observations of the timing-array millisecond pulsar PSR J0437–4715
© 2016. The American Astronomical Society. All rights reserved. Low-frequency observations of pulsars provide a powerful means for probing the microstructure in the turbulent interstellar medium (ISM). Here we report on high-resolution dynamic spectral analysis of our observations of the timing-array millisecond pulsar PSR J0437-4715 with the Murchison Widefield Array (MWA), enabled by our recently commissioned tied-array beam processing pipeline for voltage data recorded from the high time resolution mode of the MWA. A secondary spectral analysis reveals faint parabolic arcs akin to those seen in high-frequency observations of pulsars with the Green Bank and Arecibo telescopes. Data from Parkes observations at a higher frequency of 732 MHz reveal a similar parabolic feature with a curvature that scales approximately as the square of the observing wavelength (?2) to the MWA's frequency of 192 MHz. Our analysis suggests that scattering toward PSR J0437-4715 predominantly arises from a compact region about 115 pc from the Earth, which matches well with the expected location of the edge of the Local Bubble that envelopes the local Solar neighborhood. As well as demonstrating new and improved pulsar science capabilities of the MWA, our analysis underscores the potential of low-frequency pulsar observations for gaining valuable insights into the local ISM and for characterizing the ISM toward timing-array pulsars
Transformation of a Star into a Planet in a Millisecond Pulsar Binary
Millisecond pulsars are thought to be neutron stars that have been spun-up by
accretion of matter from a binary companion. Although most are in binary
systems, some 30% are solitary, and their origin is therefore mysterious. PSR
J1719-1438, a 5.7 ms pulsar, was detected in a recent survey with the Parkes
64m radio telescope. We show that it is in a binary system with an orbital
period of 2.2 h. Its companion's mass is near that of Jupiter, but its minimum
density of 23 g cm suggests that it may be an ultra-low mass carbon
white dwarf. This system may thus have once been an Ultra Compact Low-Mass
X-ray Binary, where the companion narrowly avoided complete destruction.Comment: 16 pages, 3 figures. Science Express, in pres
MWA Tied-Array Processing IV: A Multi-Pixel Beamformer for Pulsar Surveys and Ionospheric Corrected Localisation
The Murchison Widefield Array (MWA) is a low-frequency aperture array capable
of high-time and frequency resolution astronomy applications such as pulsar
studies. The large field-of-view of the MWA (hundreds of square degrees) can
also be exploited to attain fast survey speeds for all-sky pulsar search
applications, but to maximise sensitivity requires forming thousands of
tied-array beams from each voltage-capture observation. The necessity of using
calibration solutions that are separated from the target observation both
temporally and spatially makes pulsar observations vulnerable to uncorrected,
frequency-dependent positional offsets due to the ionosphere. These offsets may
be large enough to move the source away from the centre of the tied-array beam,
incurring sensitivity drops of 30-50\% in Phase II extended array
configuration. We analyse these offsets in pulsar observations and develop a
method for mitigating them, improving both the source position accuracy and the
sensitivity. This analysis prompted the development of a multi-pixel
beamforming functionality that can generate dozens of tied-array beams
simultaneously, which runs a factor of ten times faster compared to the
original single-pixel version. This enhancement makes it feasible to observe
multiple pulsars within the vast field of view of the MWA and supports the
ongoing large-scale pulsar survey efforts with the MWA. We explore the extent
to which ionospheric offset correction will be necessary for the MWA Phase III
and the low-frequency Square Kilometre Array (SKA-Low).Comment: 10 pages, 5 figure
Fluorophore tagged mixed ligand copper(II) complexes: synthesis, structural characterization, protein binding, DNA cleavage and anticancer activity
Two fluorophore tagged copper(II) complexes Cu(phen)(L)(ClO4)(2)] (1) and Cu(bpy)(L)(H2O)(ClO4)](ClO4) (2), (where L=2-amino-1H-benzode]isoquinoline-1,3-(2H)dione (L), phen=1,10-phenanthroline and bpy=2,2 `-bipyridine) have been synthesized and structurally characterized. Structures of the copper complexes 1 and 2 were confirmed by single-crystal X-ray structure determination. The coordination geometry around the copper center of complexes 1 and 2 is distorted octahedral. The plasmid DNA cleavage activity of the complexes has been investigated by agarose gel electrophoresis and the study reveals that both the complexes have high plasmid DNA photo-cleavage activity. The binding interaction ability of the metal complexes with bovine serum albumin (BSA) was investigated using fluorescence spectroscopy. The cytotoxicity of the complexes has been evaluated by MTT (3-4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide) assay against A549 (adenocarcinoma human alveolar basal epithelial cells) and MCF-7 (breast cancer cell line) cell lines in comparison with cis-platin. Complexes 1 and 2 have exhibited better cytotoxic activity than cis-platin against A549 and MCF-7 cell lines. The cellular uptake study and localization of the complexes within the cells have been investigated by fluorescence microscopy. The cell staining and flow cytometry experiments suggest that complexes induce an apoptotic mode of cell death
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